phototropism
Concise Oxford English Dictionary © 2008 Oxford University Press:
phototropism /ˌfəʊtə(ʊ)ˈtrəʊpɪz(ə)m, fəʊˈtɒtrəˌpɪz(ə)m/
▶noun Biology the orientation of a plant or other organism in response to light.
– derivatives
phototropic adjective.
phototropic adjective.
'phototropism' also found in these Oxford entries:

